Rainbows without water

Rainbows can be formed by droplets of liquids other than water, or even by a cloud of solid transparent microspheres. The table below shows the viewing angles for primary rainbows produced by a number of different media.

Refractive index
Viewing angle
Water 1.33 42.5
Kerosene 1.39 34.5
Carbon tetrachloride 1.46 26.7
Benzene 1.50 22.8
Plate glass 1.52 21.1
Other glass 1.47 to 1.61 25.7 to 14.2

Primary rainbow viewing angles for various media

  • Materials with an index of refraction of 2.00 or more do not produce primary rainbows.
  • Diamonds, for example, do not produce primary rainbows because their index of refraction is 2.42. However, if a diamond is ground into microspheres, it can produce secondary and higher-order rainbows.

Data from https://www.basic-physics.com/rainbows-figuring-their-angles/